Branched Sulfonated Polyimide/Sulfonated Methylcellulose Composite Membranes with Remarkable Proton Conductivity and Selectivity for Vanadium Redox Flow Batteries
Jun Long, Hongyan Yang, Yanlin Wang, Wenjie Xu, Jun Liu, Huan Luo, Jinchao Li, Yaping Zhang, Hongping Zhang
Abstract
Abstract A series of branched sulfonated polyimide (bSPI)/sulfonated methylcellulose (s‐MC) composite membranes composed of a designed and synthesized bSPI polymer and functionalized s‐MC are prepared by using a facile solution casting method for vanadium redox flow batteries (VRFBs). Among all bSPI/s‐MC composite membranes, the optimized bSPI/s‐MC‐20 % composite membrane has the best proton selectivity of 2.45×10 5 S min cm −3 , which is 14.4 times as high as the Nafion 115 membrane. The bSPI/s‐MC‐20 % composite membrane possesses superior proton conductivity compared to most reported SPI‐based composite membranes for VRFBs. The VRFB with a bSPI/s‐MC‐20 % composite membrane shows excellent battery efficiencies ( CE =99.2–98.0 %, EE =66.3–77.6 %) and capacity retention (73.3–47.2 %). Moreover, the cost of the bSPI/s‐MC‐20 % composite membrane is only a quarter of that of a commercial Nafion 115 membrane. This work develops a new strategy to fabricate cheap bSPI‐based composite membranes by introducing a suitable functionalized biomass material.